depression has many causes and some are biological. when depression is biological its exacerbates the tensions in your life re enforcing them and can dissuade you from doing things to help yourself. there are many kinds of depression, biological and existential, and most overlap in symptoms and causes. i cant really explain it in the detail thats needed for a real understanding here as it would take forever and would require responses/dialogue in order for you to really understand so if you do want to understand why material doesnt always make people happy youd have to do some research and theres a lot of accurate open sources online for you to draw from including the new standard d.s.m. check it out as understanding and knowledge is always a good thing.
that said ive no idea if he really is clinically depressed or depressed at all. just speculation based on absence and gossip but i worry.